Humidity cabinet with automatic fluid fill system

ABSTRACT

A fluid fill system includes at least one sensor for indicating whether a fluid level in a reservoir is equal to or greater than a predetermined fluid level and a process control. The process control obtains a reading from the at least one sensor at a predetermined interval and increments a counter if the reading indicates that the fluid level is equal to or greater than the predetermined fluid level and decrements the counter if the reading indicates that the fluid level is less than the predetermined fluid level. Process control operates a fluid supply mechanism when a value of the counter moves beyond a predetermined value.

The present application is a continuation-in-part of U.S. applicationSer. No. 09/671,700, entitled “Holding Cabinet with Closed-Loop HumidityControl System and Method for Controlling Humidity in a HoldingCabinet,” filed Sep. 28, 2000, now U.S. Pat. No. 6,454,176, which claimspriority from U.S. Provisional Patent Application No. 60/217,707,entitled “Holding Cabinet with Closed-Loop Humidity Control System andMethod for Controlling Humidity in a Holding Cabinet,” filed Jul. 12,2000, and U.S. Provisional Patent Application No. 60/156,449, entitled“Holding Cabinet with Closed-Loop Humidity Control System and Method forControlling Humidity in a Holding Cabinet,” filed Sep. 28, 1999, whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a holding cabinet, which provides amore consistent and accurate holding environment for food products. Inparticular, the invention relates to a holding cabinet, which provides amore consistent and accurate holding environment for food products bymaintaining a desired fluid level in a fluid reservoir.

2. Description of Related Art

With the increasing popularity of “fast food” establishments where foodis precooked for later sale, there is a demand for food holding devicesthat maintain food at a substantially uniform temperature for selectedperiods of time while preserving the taste, moisture content, textureand quality of the food. Further, in other applications, it is desirableto be able to restore food, particularly baked goods, to acceptablequality after long storage periods.

In many instances, storage of “fast foods” is particularly difficultbecause heat loss, bacteria growth and moisture loss experience by thefood at storage conditions provided by prior art devices, particularlywhere the food is to be stored warm, contribute to rapid deteriorationof the food.

More particularly, it has been found that air circulationcharacteristics and improper storage temperature contributesignificantly to bacteria growth and excessive loss of moisture whichleads to food shrinkage, so that in improper storage atmosphere the fooddeteriorates after only a short period of time and loses its tenderness,appetizing taste, and appearance.

It has also been found that even where food is stored under favorableconditions in an enclosure, the food deteriorates at a rate dependent onthe time the door to the enclosure is opened so the storage chamber isexposed to the ambient atmosphere.

Additionally, it is known that in storage of some foods, such as friedchicken or fish, where a crust is provided, it is particularly desirableto maintain the crispness of the crust while minimizing the moistureloss from the underlying meat. Storage of such foods tends to involvethe satisfaction of seemingly mutually exclusive conditions, to hold thecrispness of the crust by maintaining low moisture content in the crustwhile minimizing moisture loss from the food. In such foods, excessivemoisture-loss results in shrinkage and loss of tenderness and adverselyaffects the texture of the meat. This may be prevented by controllingthe temperature and humidity of the storage atmosphere. The problem isto prevent moisture flow from the underlying food to the crust whileholding the crust in low moisture content.

There are presently numerous cabinets for holding food products or otheritems in a temperature and humidity-controlled state. These cabinets,however, suffer from a common shortcoming. When the cabinets are openedto insert additional food products or other items or to remove suchproducts or items from the cabinets, heat and humidity are lost. Unlessthe lost heat and humidity is restored, the items stored in the cabinetsmay cool or dry out, or both.

Proofing and holding are distinct food preparation processes. Proofingis a process generally applied to yeast bread products, in which theyeast grows and the bread rises due to yeast growth by products.Holding, however, is a process during which food characteristics aremaintained, e.g., the temperature, moisture content, texture, and colorof the food remain unchanged. Thus, in proofing, food productcharacteristics change, while in holding, those characteristics remainthe same.

In terms of process parameters, proofing may be distinguished fromholding mainly by lower process temperatures. Humidity may be greaterthan about 80% RH, but the selected humidity may vary widely dependingon the particular bread product to be proofed. Nevertheless, proofingtemperatures are generally lower than holding temperatures. Highproofing temperatures might inhibit yeast growth. However, high holdingtemperatures are desirable because such temperatures may suppress thegrowth of bacteria, molds, and the like and may increase the holdingtime for food products.

Previously, various methods and devices have been developed to attemptto maintain heat and humidity. For example, pans of water have beenplaced in the cabinets and allowed to evaporate naturally in an attemptto maintain humidity. Despite its simplicity, this method has not beencompletely successful. Natural evaporation does not quickly compensatefor humidity losses. Further, while humidity naturally increases, itemsstored in the cabinets are subject to the drying effect of heat.Moreover, because natural evaporation is effected by the temperaturewithin the cabinet, the rate of humidity adjustment may fluctuate withtemperature changes, but humidity adjustments will probably lag behindsuch temperature changes.

Systems have been developed by which the heat and humidity levels of airwithin a cabinet are more closely controlled. Air may be heated bypassing it over, across, or through various types of heating elements.Air may also be passed over, across, or through water in order to raisethe humidity of the air. Despite these improvements, known systemsremain unable to precisely adjust for losses of heat or humidity due todisruptions to the cabinet environment, such as opening and closing thecabinet access, and adding or removing food products or other items.

Further, the addition of heating elements and humidity generating meanscreate additional problems. If heat or humidity rise too quickly, theair within the cabinets could become overheated or too moist. Suchuncontrolled fluctuations in heat and humidity may be detrimental tofood product or other items stored within the cabinets.

Cabinets commonly are equipped with thermostats in an attempt to controlthe heat of the air circulating within the cabinets. By controlling theair temperature, however, the humidity of the air also may be affected.Nevertheless, such controls alone do not provide adequate control of thehumidity within the cabinet. Moreover, a thermostat or manualpotentiometer may not maintain temperature and humidity withinpredetermined parameters. Generally, such devices only cause the heatingelements to heat the air when the air temperature falls below a setvalue.

The effectiveness of humidity generating systems depends, in part, onthe ability of those systems to maintain fluid in a fluid reservoir, sothat the fluid in the reservoir may be heated, e.g., heated to a boilingpoint, to produce a fluid vapor. The fluid vapor may be circulatedthrough holding or proofing cabinets to create and maintain a desiredlevel of humidity. A fluid supply mechanism may supply fluid to thefluid reservoir. A problem may arise, however, if fluid is notmaintained in the reservoir, so that holding or proofing cabinets may behumidified. For example, a fluid level sensor may not accurately measurea fluid level in a reservoir. The fluid supply mechanism or the fluidlevel sensor may become inoperative. As a result, the reservoir maybecome empty, and the humidity generating system may not humidify theholding cabinets.

A further problem may arise when fluid is added to a reservoir. As fluidis added to the reservoir, fluid levels within the reservoir mayfluctuate due to fluid turbulence. As a result, a fluid level sensor maydetect relatively rapidly changing fluid levels within the reservoir. Asthe level of fluid in reservoir approaches a level at which thereservoir is considered to be full, the fluid level sensor may detectfluid levels that indicate alternately that the reservoir is full andthat the reservoir is not yet full, depending upon the level ofturbulence in the reservoir. If an automatic fill system controls thefluid supply mechanism to supply fluid to the reservoir based on fluidlevels detected by fluid level sensor, the alternating signals mayresult in damage to various components of the fluid supply mechanism,e.g., fluid pumps, fluid motors, valves, or the like, as the componentscycle on and off in response to the alternating signals of the fluidlevel sensor. Moreover, when the components cycle on and off in responseto alternating signals of fluid level sensor, the cycling of thecomponents may create additional turbulence and additional fluctuationsin fluid level sensor.

SUMMARY OF THE INVENTION

A need has arisen for holding cabinets for attaining closed-loophumidity control by means of an effective humidity transducer. A furtherneed has arisen for a cabinet that may be used for both proofing andholding. It is a feature of such a cabinet that its control systemdefaults to a generally higher temperature associated with a holdingmode of operation. It is an advantage of this default setting that thecabinet may inhibit the growth of bacteria in food products.

A still further need has arisen for a fluid fill system and method thatmeasure a fluid level in a reservoir accurately and that maintain thefluid level within a reservoir, so that a humidity generating system mayhumidify one or more holding or proofing cabinets. In particular, a needhas arisen for a system and method of filling a fluid reservoir, so thatfluid in the reservoir may be maintained at a desired level and so thatdamage to components of a fluid supply mechanism may be reduced oravoided.

In an embodiment of the invention, a holding cabinet with a closed loophumidity control system and a method of controlling humidity in aholding cabinet are disclosed. The method comprises determining relativehumidity set points; activating a heater in a fluid pan; determining ifa fluid is present in the fluid pan; measuring the relative humidity inthe cabinet; and maintaining the relative humidity within apredetermined range.

According to another embodiment of the invention, a holding cabinet witha closed-loop humidity control system includes a holding cabinet; an airtemperature probe for measuring an air temperature within the holdingcabinet; a humidity sensor for measuring a humidity within the holdingcabinet; a heater for heating air within the holding cabinet to apredetermined temperature; a fan for circulating the air and forintroducing air from outside the holding cabinet; a slide vent andmotor; and a water pan for holding water within the holding cabinet.

According to still another embodiment of the invention, a system forhumidity measurement includes a humidity sensor; an oscillator circuit;and a microprocessor to measure oscillator frequency. According toanother embodiment of the invention, a system for maintaining a relativehumidity level in a cabinet includes means for determining a relativehumidity set point; means for activating a heater in a fluid pan; meansfor determining if a fluid is present in the fluid pan; means formeasuring the relative humidity in said cabinet; and means formaintaining the relative humidity within a predetermined range.

In yet a further embodiment of the invention, a fluid fill systemcomprises at least one sensor for detecting whether a fluid level in areservoir is equal to or greater than a predetermined fluid level, and aprocess control, wherein the process control obtains a reading from theat least one sensor at a predetermined interval and increments a counterif the reading indicates that the fluid level is equal to or greaterthan the predetermined level and decrements the counter if the readingindicates that the reservoir fluid level is less than the predeterminedfluid level, and wherein the process control operates a fluid supplymechanism when a value of the counter moves beyond a predeterminedvalue.

In a still further embodiment of the invention, a method of filling areservoir with a fluid comprises the steps of obtaining a fluid levelreading at a predetermined interval to determine whether a fluid levelin a reservoir is equal to or greater than a predetermined level,incrementing a counter if the fluid level reading is equal to or greaterthan the predetermined level, decrementing the counter if the fluidlevel reading is less than the predetermined level, and operating afluid supply mechanism when a value of the counter moves beyond apredetermined value.

Other objects, features, and advantages will be understood by personsskilled in the art from the following detailed description of preferredembodiments of the present invention, in view of the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described below with reference to theaccompanying figures, which are provided by way of example only, and arenot intended to limit the present invention.

FIG. 1 depicts a front view of the holding cabinet according to anembodiment of the present invention.

FIG. 2 depicts a side view of the holding cabinet according to anembodiment of the present invention.

FIG. 3 depicts a cross-sectional view of the holding cabinet of thepresent invention, along line III—III of FIG. 1.

FIG. 4 depicts a cross-sectional view of the holding cabinet of thepresent invention, along line IV—IV of FIG. 2.

FIG. 5 is a schematic depiction of the air and humid air circulationwithin the holding cabinet according to an embodiment of the presentinvention.

FIG. 6 is a perspective view of a water pan cover and ring assemblyaccording to an embodiment of the present invention;

FIG. 7 is a schematic depiction of the humidity generating pan and thecontrol and monitoring interconnections of the holding cabinet accordingto an embodiment of the present invention.

FIG. 8 depicts the circuitry of the humidity detection transduceraccording to an embodiment of the present invention.

FIGS. 9A and 9B are side and top views of a slide vent according to anembodiment of the present invention.

FIGS. 10A and 10B are schematic depictions of the slide vent and cabinetopenings according to an embodiment of the present invention.

FIG. 11 is a flowchart of the process for vent operation according to anembodiment of the present invention.

FIG. 12 is a flowchart of the calibration process for the slide ventmotor according to an embodiment of the present invention.

FIG. 13 is a depiction of the period of the slide vent according to anembodiment of the present invention.

FIG. 14A depicts a humidity regulation state diagram according to anembodiment of the present invention.

FIG. 14B is a graphical representation of the humidity control processaccording to an embodiment of the present invention.

FIG. 15 is a flowchart of the process for increasing humidity accordingto an embodiment of the present invention.

FIG. 16 is a flowchart depicting the operation of the closed-loophumidity control system.

FIG. 17 shows a fluid fill system according to an embodiment of theinvention.

FIG. 18 is a flowchart depicting the operation of a fluid fill systemaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention and their technical advantages maybe better understood by referring to FIGS. 1 though 13, like numeralsreferring to like and corresponding parts of the various drawings.

Referring to FIGS. 1 and 2, a front view of the holding cabinet and aside view of the holding cabinet according to an embodiment of thepresent invention are provided. Holding cabinet 100 has a front 102,back 104, and sides 106 and 108. Front 102 and back 104 may both have atleast one door with a corresponding locking mechanism 110. In theembodiment depicted in FIGS. 1 and 2, front 102 and back 104 each havetwo doors.

Module 114 is provided to house equipment used to control the relativehumidity in cabinet 100. In an embodiment, holding cabinet 100 may beprovided with a plurality of wheels 112.

Referring to FIG. 3, a cross-sectional view of the holding cabinet ofthe present invention, along line III—III of FIG. 1 is provided.Referring to FIG. 4, a cross-sectional view of the holding cabinet ofthe present invention, along line IV—IV of FIG. 2 is provided.

Referring to FIG. 5, a schematic depiction of the air and humid aircirculation within the holding cabinet according to one embodiment ofthe present invention is provided. Blower motor 708 is provided, as areheaters 706. In the embodiment shown, two heaters 706 are provided;other numbers and locations of heater 706 may also be used.

Water pan 316 is provided with water pan cover and ring assembly 502,which is shown in detail in FIG. 6. Water pan cover and ring assembly502 includes inner ring 520, outer ring 522, and cover 524. Steamexhaust ports 526 may be provided. In one embodiment, two exhaust ports526 are provided, at opposite sides of the rings.

Referring again to FIG. 5, water pan in water pan 316 is heated by awater pan heater 506, which causes the water in water pan 316 tovaporize into steam 504. Inner and outer rings 520 and 522 of assembly502 concentrate heat generated by water pan heater 506, assisting in thevaporization.

FIG. 7 depicts a block diagram of system 700 according to an embodimentof the present invention. System 700 includes air temperature probe 702,which measures the temperature of the air in the holding cabinet. Airtemperature probe 702 may also be used to provide temperaturecompensation for humidity sensor 704 In one embodiment, air temperatureprobe 702 may be part number DC32006A-3-18, manufactured by DurexIndustries, Cary, Ill.

Humidity sensor 704 measures the relative humidity of the air in thecabinet (H1). In an embodiment, humidity sensor 704 may be E&EElectronik Part No. EE00-FR3, manufactured by JLC International,Warminster, Pa. Air heater 706 heats the air in the cabinet to the setpoint specified by the user. In one embodiment, air heater 606 may bepart number U3-32-764-34, 500 W, 1000 W, or 1500 W, manufactured byWatlow, Hannibal, Mo. Air fan 708 circulates heated air through thecabinet so that the entire cabinet volume is at the same temperature. Inone embodiment, air fan 708 may be part number SX-19695 (240V) orSX-20441 (208V), manufactured by Jakel, Highland, Ill.

Water pan 716 holds water to be boiled to create humidity. In oneembodiment, water pan heater 722 may be #-8-MSM22866-xxx, manufacturedby Minco, Minneapolis, Minn. In another embodiment, heating elements maybe screened onto water pan 716. Float switch 720 is provided todetermine the water level in water pan 716. In an embodiment, floatswitch 720 may control water flow into water pan 716 when the waterlevel is below a desired level. An water pan heater (RTD) temperaturesensor 723 is affixed to water pan heater 722. Alternatively, sensor 723may be integral with heater 722. Sensor 723 may measure the temperatureof heater 722 and input such measured temperature values to System 700.

Water pan heater temperature sensor 723 is linked to control system 700to ensure that water pan heater 722 remains off when either of at leasttwo conditions occurs: first, when no water is in water pan 716 orsecond, when float switch 720 fails. In normal operation, float switch720 signals control system 700 that water pan 716 is empty, so controlsystem 700 does not activate water pan heater 722. Nevertheless, linebuild-up, debris, or abuse may cause float switch 720 to fail in the“full water pan” position. Water pan 716 and water pan heater 722 may bequickly damaged if water pan heater 722 is activated while water pan 716is empty. Water pan heater temperature sensor 723 performs as a backupto float switch 720 to reduce or eliminate the risk of such damage towater pan 716 or water pan heater 722, or both.

Slide vent motor 730 controls the movement of the slide vent, which, inturn opens and closes the cabinet vent. Slide vent position switch 732is provided to provide an indication of the status of the vent. In oneembodiment, side vent position switch 732 may be part number KWABQACC,manufactured by Cherry Electrical Products, Pleasant Prairie, Wis.Switch 732 may also be an switch, optical proximity switch.

Process inputs and outputs connect to the process control as shown.Temperature sensor 798 is built into heater 722 and measures the waterpan temperature.

The cabinet air temperature is regulated with air temp sensor 702, airheater 706 and air fan 708. The air temp regulation is obvious to thoseskilled in the art, and consists simply of regulating the airtemperature to the programmed set point. This may be a simplethermostatic (on/off) control with hysteresis, or may be a moresophisticated PID (proportional/integral/derivative) control algorithm.

Humidity may be regulated by 1) adding humidity when the cabinethumidity is below the humidity set point, and 2) decreasing humidity byintroducing outside ambient air to the cabinet, when the cabinethumidity is above the programmed set point. Thus, there are two separatesystems to regulate the humidity: a humidity generation system, and a“venting” system.

Referring to FIG. 8, humidity transducer circuit 800 according to oneembodiment of the present invention is provided. Timer U1 forms anastable oscillator with output frequency, F_(O), set by capacitorsC_(x), C₁, and resistor R₁. Capacitors C₂ and C₃ bypass power supply.Capacitor C₁ blocks DC voltage to transducer C_(x), which is damaged byDC voltage. Resistor R₁ sets the frequency, F_(O). Resistor R₂ drainscharge from capacitor C₁ during power-down. Transducer C_(x) capacitancevaries with humidity. Microprocessor μP measures F_(O) period bycounting pulses (n₂) for {fraction (1/16)} second.

Example values for the elements in FIG. 8 are provided below:

Element Value U1 LMC 555 C Timer R₁ 24.9 K R₂ 5 M C₁ .039 μF, 50 V, 1%,100 PAM C₂ 0.1 μF ceramic disk C₃ 10 μF Tantalum C_(X) HumidityTransducer, E & E Electronik EE00-F123

The relative humidity percentage (% RH) may be determined by thefollowing equation:${\% \quad R\quad H} = {419.734\quad \left( {\frac{4343.287}{n_{2} + 360} - 1} \right)}$

Capacitance C_(x) also is affected by temperature, therefore, % RH iscompensated for temperature with this equation:

%RH _(C)=[(T _(F)−140)(0.0016667)+1](%RH)

where:

T_(F) is air temperature in ° F. % RH_(C) is used to display andregulate humidity.

The systems of the present invention may implement a proofing mode ofoperation. As noted above, this invention may combine the proofing andholding functions in a single cabinet. For example, on initiation of anypower-up condition, a user interface, e.g., a display, for the controlsystem may offer the user the opportunity to initiate a “Proof” option.The user may have a limited time window, e.g., ten (10) seconds, withinwhich to accept this option. The user may accept the option byactivating a particular switch, e.g., a TEMP switch, or a combination ofswitches. If the option is not accepted during the time window, thecontrol system initiates the hold (higher temperature) mode. However, ifthe option is accepted, the control system initiates the proof (lowertemperature) mode.

The bold and proof modes are distinguished by the maximum allowable airtemperature set point. For example, in the proof mode, the maximumallowable air temperature set point may be the minimum hold temperature.Thus, if the minimum hold temperature were 150° F., the maximum prooftemperature setpoint would be 150° F. Similarly, if the minimum holdtemperature were 150° F., the maximum allowable hold mode airtemperature set point might be 220° F., and the hold mode temperaturerange might be 150° F. to 220° F.

Referring to FIGS. 9A and 9B, side and top views of a slide ventaccording to an embodiment of the present invention are provided. Ingeneral, cabinet panel 902 is provided with slide panel 904. Bothcabinet panel 902 and slide panel 904 have at least one opening 906 Inone embodiment, openings 906 in cabinet panel 902 are fixed, whileopenings 902 in slide panel 904 slide relative to openings 906 incabinet panel 902. Gear motor 908 drives slide panel 904 linearly toopen or close openings 906 via lever arm 912 and slide pin 914. In oneembodiment, motor 908 is model number EB-5206, manufactured by CustomProducts, Inc., New Haven, Conn., or part number AB, manufactured byHurst Manufacturing Corporation, Princeton, Ind.

As slide panel 904 slides relative to cabinet panel 902, openings 906 onslide panel 904 line up with openings 906 on cabinet panel 902, ineffect opening a passage to the blower inlet and outlet (not shown).When slide panel 904 slides its full distance, openings 906 in cabinetpanel 902 are fully uncovered. At this point, slide panel 904 beginssliding in the opposite direction, and openings 906 in cabinet panel 902are covered, blocking access to the blower inlet and outlet (not shown).

Switch 916 is provided to indicate when vents 906 are fully closed. Inanother embodiment, switch 916 may be provided to indicate when vents906 are fully opened. This variance may depend on the position of switch916 with respect to slide 904. Other arrangements may be provided asdesired. Switch 916 may be used during calibration to determine theperiod of slide vent 904. This is discussed in greater detail, below.

Referring to FIGS. 10A and 10B, depictions of the slide vent in itsclosed and open positions are provided, respectively. In FIG. 10A, slidevent 904 is positioned such that air does not flow from the exterior ofthe cabinet into blower inlet 1010, and out of blower exhaust 1012. Whenmotor 908 is activated, however, slide vent 904 is moved, shown in FIG.10B, opens blower inlet 1010 and blower exhaust 1012.

Referring to FIG. 11, a flowchart of the general operation of thecabinet is provided. In step 1102, the cabinet is powered up. This mayinvolved initializing cabinet components, which is known to one ofordinary skill in the art.

In step 1104, the vent motor is calibrated. This process is described ingreater detail in FIGS. 12 and 13, below.

Referring to FIG. 12, a flowchart of the slide vent motor calibrationprocess according to one embodiment of the present invention isprovided. The purpose of the calibration is to account for variations inthe actual time required to move the vent from one position to another.Even though a synchronous AC motor may be used, the time for onerevolution may vary because 1) the line frequency may be 50 Hz or 60 Hz,and 2) friction and debris in the mechanism may slow the vent movement.

In general, the control software needs to know the time for one completerevolution to be able to move the vent from the fully-opened to thefully-closed position. The control knows when the vent is fully-closed,because a vent switch actuates at that position. Thus, if the actualperiod for the vent movement is T_(VENT), then the vent is fully open attime T_(VENT)/2. Also, the control may move the vent to other positions,such as 50% open area, by actuating the motor for some time that is afraction of T_(VENT). For example, to open the vent to about 50% openarea, the control activates the motor for about T_(VENT)/4, from eitherthe fully-open or fully-closed position.

In one embodiment, although the vent open area is not a linear functionof the vent motor actuation time, it provides a suitable approximation,permitting the vent motor actuation time to be used to position theslide vent. In another embodiment, different shapes for the vent holesmay be used to provide a linear relationship between motor actuationtime and vent open area.

FIG. 13 depicts the vent operation as far at the control is concerned.As the motor turns and the vent actuates the vent switch, the ventswitch is really actuated for some period of time, which may be referredto as the “dwell time,” or T_(DWELL). The control may account forT_(DWELL) when calculating the time needed to actuate the motor toachieve a given vent position.

Referring again to FIG. 12, in one embodiment, the vent calibrationroutine uses a timer that is always running, so there is no need tostart or stop the timer, just a need to reset it to find the dwell timeand the period. In step 1202, there is a predetermined delay, duringwhich timers and interrupts are synchronized. In one embodiment, thismay be a one second delay; other delays may be used, as required. Inanother embodiment, this delay may be omitted.

In step 1204, after the timers and interrupts are synchronized, the ventmotor is activated, causing the slide vent to move. The timer is clearedin step 1206, and, in step 1208, the control waits for a firsttransition signal from vent switch. This signal indicates that the ventswitch is being activated. If there is no switch signal within apredetermined time, an error message is presented to the user in step1210. This may be by a visual or audible signal, such as a CRT, a LED, abell, a chime, and the like. In an embodiment, a suitable message, suchas “Vent Stuck” is displayed for the user.

In one embodiment, the predetermined amount of time may be 48 seconds.Other suitable lengths of time may be used as desired. This time may beselected based on, inter alia, the known general period of the vent. Thetime may also be selected to prevent damage to the motor. After thepredetermined time is elapsed, the motor may be shut off.

If a signal is received from the vent switch, in step 1208, the timer iscleared, and in step 1214, the control waits for a second transitionsignal from the vent switch, indicating that the vent switch is nolonger actuated. Similar to above, if a predetermined time passeswithout a signal from the vent switch, the user may be notified in step1210. Once the second transition signal is received, in step 1216, thetimer is read, indicating the dwell time, or T_(DWELL). In step 1220,similar to steps 1208 and 1214, the control waits for a transitionsignal from the vent switch. Once a transition signal is received,indicating that the vent has completed its cycle, in step 1222, thetimer is read. This is T_(VENT).

In step 1224, the vent is moved to the fully-closed position. Asdiscussed above, this may be achieved by activating the motor forT_(VENT)/2.

The control may use the time required to move the vent to detect faultsin the vent system. If it takes longer than a predetermined time for onecomplete revolution, the control assumes that the vent is stuck, or themotor has failed, and displays a fault message.

Referring again to FIG. 11, in step 1106, the control determines if thevent position is within a predetermined tolerance of its requestedposition. In an embodiment, the vent position may be expressed as anopening percentage—from 100% open, to 0% open. In this step, it isdetermined if the actual position is within a predetermined window ofthe desired position. This may be about 10%, 5%, 2%, and the like. Inone embodiment, it is about 1%. If the vent is within this window, noadjustments are made.

If, in step 1108, it is determined that the vent is not within thepredetermined window, the vent motor is activated for a determinedamount of time to move the vent to its desired position.

In step 1110, the device may be powered down. When this occurs, it ispossible that humidity may condense on the humidity sensor as the airtemperature within the cabinet drops. This may 1) damage the humiditysensor, or 2) cause false humidity readings during operation. In orderto compensate for this problem, in one embodiment, the device enters“purge” mode that is activated when the control switch is changed from“operate” to “standby” or “off.” In this mode, the air heater and thewater heater are turned off, and the fan is activated if the humidity isgreater than a predetermined level. The predetermined humidity level maybe selected as a compromise between low humidity (much lower than 100%)and high ambient humidity that exists within restaurants or otheroperating environments. In one embodiment, this percentage may be 80%.

When the fan is activated, air from outside the cabinet is injected intothe cabinet, for the most part, preventing the humidity in the cabinetfrom exceeding the predetermined level. In general, controlling thehumidity in the cabinet involves regulating the water heat output andthe vent motor output. The water heat output is usually turned on toincrease humidity within the cabinet, while the vent is usually openedto reduce humidity within the cabinet.

According to an embodiment of the present invention, the humiditycontrol method consists of three states: Idle, Increase Humidity, andDecrease Humidity. Referring to FIG. 14A, a humidity regulation statediagram is provided. In the decrease humidity state, the vent is eitheropen 50% or 100%, depending on how far the actual humidity is above theset point. Other opening percentages may be used as desired. FIG. 14Bprovides a graphical representation of the humidity regulation.

In addition, the control levels of SP+9% RH and SP+7% just amount to ahysteresis band that switches between about 50% and about 100% ventopening.

In the Increase Humidity state, the net result of the flow chart logicis to determine a duty cycle setting for the water heat output. The dutycycle is the number of {fraction (1/16)} second intervals, out of aperiod of 2 seconds that the water heat is on. For example, in a dutycycle of 25%, the heat is on for 0.5 seconds, which is 8 intervals of{fraction (1/16)} second. Referring to FIG. 15, a flowchart depictingthe Increase Humidity logic according to one embodiment of the presentinvention is provided.

The humidity control is similar to PID control, but the derivativeinformation is only used to update the integral term.

Blocks 1502 to 1508 set the water heat duty cycle when the actualhumidity is the same as the set point. If the temperature is below 125°F., the duty cycle is set to 25%. If the temperature is above 125° F.,the duty cycle is set to 31%. These cycles act to maintain the humiditynear the set point. A higher duty cycle is needed at highertemperatures. Blocks 1510 and 1512 set the duty cycle to 100% (full on)if the actual humidity is more than 3% RH below the humidity set point.This acts to bring the humidity back to the set point. Block 1514calculates the humidity error (humidity set point-actual humidity) andsaves it in a variable called hum_temp_byte.

Blocks 1516-1526 adjust the integral correction term I.E.L (which standsfor the code variable integral_error_level). The test in block 1516limits I.E.L. to values of 20 and 200. Block 1518 adds the humidityerror to I.E.L. Blocks 1520- to 1526 add 5 to I.E.L. if the humidity isdecreasing, and subtract 20 from I.E.L. if the humidity is increasing.

The initialization of I.E.L. is not shown, but I.E.L. is set to zerowhenever the Increase Humidity state is entered, or whenever themeasured humidity equals the set point.

The blocks in 1528 set a new variable, E.O. (for error_offset) from thevalue of I.E.L. just found. Note that a larger value of I.E.L. resultsin a larger value of E.O.

The blocks in 1530 find the duty-cycle on-time, called t(on). t(on) is afunction of E.O. and the air temperature Ta. t(on) is just the sum of aconstant that depends on the air temperature and the value of E.O.

Finally, block 1532 show that the actual duty cycle is calculated fromt(on)/31. The divisor is “31” because a 16 Hz clock is used for thewater heat output. The duty-cycle period is 2 seconds, but the clockactually counts from 0 to 31.

Referring to FIG. 16, a flow chart of the operation of a closed-loophumidity control system is depicted. In this chart, T_(H) is the waterpan heater temperature measured by water pan heater temperature sensor723, and T_(UM) is the maximum allowable water pan temperature. AFloat-Switch-Fault is true when float switch 720 has failed. Floatswitch 720 has failed when it fails to accurately detect significantchanges in the water level in water pan 716.

Various operational conditions are detailed with respect to FIG. 16. Ifwater pan 716 is found empty during normal operations, float switch 720will indicate allow water level (Step B) and a “low water level” messageis displayed (Step F). Water pan heater 722 then will be disabled (StepI), and control system 700 will complete its operation (Step L).

Similarly, if water pan 716 is incorrectly found empty during normaloperations, float switch 720 again will indicate a low water level (StepB). However, control system 700 will inquire whether T_(H>)T_(LIM) (StepC). If T_(H)≦T_(LIM), the Float-Switch-Fault is true (Step D), and waterpan heater 722 is enabled (Step J). Control system 700 then againcompletes its operation (Step L).

If a Float-Switch-Fault is detected, a low water level is again detected(Step B) and control system 700 again will inquire whether T_(H>)T_(LIM)(Step C). If T_(H)>T_(LIM), then water pan 716 is empty or low on waterand Float-Switch-Fault is true (Step E). The display may then indicate“Float Switch Failed” and “Out of Water” or “Pan Empty” (Step G). Waterpan heater 722 will be disabled (Step I), and control system 700 willcomplete its operation (Step L).

While waiting for a Float-Switch-Fault to clear, Float switch 720 willinitially indicate that the water level in water pan 716 is low (StepB). Control system 700 then will inquire whether T_(H>)T_(LIM) (Step C).If T_(H)≦T_(LIM) then Float-Switch-Fault is true (Step D), and ifwhether T_(H>)(T_(LIM)−100° F.) or the reset delay timer is not set tozero (Step H), water pan heater 722 is disabled (Step I). Control system7800 then will complete its operation (Step L).

Once the Float-Switch-Fault has cleared, if Float switch 720 indicatesthat the water level in water pan 716 is low (Step B), control system700 inquires whether T_(H>)T_(LIM) (Step C). If T_(H)≦T_(LIM), thenFloat-Switch-Fault is true (Step D), and control system 700 inquireswhether T_(H>)(T_(LIM)−100° F.) and whether the reset delay timer is setto zero. (Step H). If both these conditions exist, theFloat-Switch-Fault is false (Step K), and water pan heater 722 isenabled (Step J). Control system 700 then will complete its operation(Step L).

FIG. 17 shows a fluid fill system 1700 according to an embodiment of theinvention. Fluid fill system 1700 includes a reservoir 1701, a fluidsupply line 1702, a fluid supply mechanism 1703, a fluid level sensor1704, and a process control 1705.

Fluid reservoir 1701 is capable of holding a fluid, such as water, forthe humidity control system. Fluid reservoir 1701 may include a pan,container, or the like, that is capable of receiving and holding afluid, such as water. Fluid may be supplied to reservoir 1701 by a fluidsupply line 1702. Fluid supply line 1702 may include a fluid supplymechanism 1703, e.g., a fluid supply valve 1703. Fluid supply mechanism1703 may be positioned in fluid supply line 1702 to open fluid supplyline 1702, so that fluid may be supplied to reservoir 1701, or to closefluid supply line 1702, so that fluid may be prevented from flowing toreservoir 1701. Fluid supply mechanism 1703 may include a solenoid valvethat may be actuated to open and close fluid supply line 1702. Inanother embodiment of the invention (not shown), fluid supply mechanismmay include a pump that supplies fluid to reservoir 1701, via fluidsupply line 1702. Fluid supply line 1702 may include one or more fluidsupply lines 1702 that supply fluid to reservoir 1701.

A fluid level sensor 1704, e.g., a float switch or the like, may bepositioned in reservoir 1701 to detect, e.g., to measure, or the like,the level of fluid in reservoir 1701. In an embodiment of the invention,fluid level sensor 1704 may detect a level of fluid in reservoir 1701and indicate whether the fluid level within reservoir 1701 is equal toor greater than a predetermined level. The predetermined level maycorrespond to a fluid level at which reservoir 1701 is considered to befull. In this embodiment, fluid level sensor 1704 has two states: afirst state indicating that a fluid level in reservoir 1701 is equal toor greater than a predetermined level and a second state indicating thata fluid level in reservoir 1701 is less than the predetermined level.When the fluid level in reservoir 1701 is equal to or greater than thepredetermined level, fluid level sensor 1704 will so indicate. When thefluid level in reservoir 1701 is less than the predetermined level,fluid level sensor 1704 will so indicate. Fluid level sensor 1704 may beadjusted to detect different predetermined fluid levels, as necessary. Afloat switch or the like may be used as a fluid level sensor 1704 todetect fluid levels in reservoir 1701. Moreover, more than one fluidlevel sensor 1704 may be positioned in reservoir 1701.

Process control 1705 may include a processor, a microprocessor, or thelike. Process control 1705 may communicate with fluid supply mechanism1703 to operate fluid supply mechanism 1703, e.g., to activate ordeactivate fluid supply mechanism 1703. Process control 1705 may operatefluid supply mechanism 1703 to supply fluid to reservoir 1701, orprocess control may operate fluid supply mechanism 1703 to stop a supplyof fluid to reservoir 1701. For example, process control 1705 mayoperate fluid supply mechanism 1703 to supply fluid to reservoir 1701 byactivating a fluid supply valve 1703 to open fluid supply line 1702, sothat fluid may be supplied to reservoir 1701. Process control 1705 mayoperate fluid supply mechanism 1703 to stop supplying fluid to reservoir1701 by deactivating fluid supply valve 1703 to close fluid supply line1702. By selectively activating and deactivating fluid supply mechanism1703, process control 1705 may adjust a level of fluid in reservoir1701.

Fluid level sensor 1704 may communicate with process control 1705, sothat process control 1705 may monitor a level of fluid in reservoir1701. Process control 1705 and fluid level sensor 1704 may communicatein a variety of ways. For example, process control 1705 may query fluidlevel sensor 1704 at a predetermined interval to obtain readings of afluid level in reservoir 1701, so that process control 1705 may monitora level of fluid in reservoir 1701. Each reading of fluid level sensor1704 may indicate whether the level of fluid in reservoir 1701 is equalto or greater than a predetermined level, or whether the fluid level inreservoir 1701 is less than the predetermined level. In anotherembodiment of the invention, fluid level sensor 1704 may detect a fluidlevel in reservoir 1701 at a predetermined interval and transmit eachreading to process control 1705, so that process control 1705 maymonitor a fluid level in reservoir 1701. Each reading from fluid levelsensor 1704 may indicate whether the level of fluid in reservoir 1701 isequal to or greater than a predetermined level, or whether the fluidlevel in reservoir 1701 is less than the predetermined level. Moreover,the predetermined interval may be selected from a range of predeterminedintervals, so that process control 1705 may obtain readings from fluidlevel sensor 1704 at different frequencies.

In either embodiment, fluid level sensor 1704 may communicate withprocess control 1705 at a predetermined interval, so that processcontrol 1705 may obtain fluid level readings that correspond to a levelof fluid in reservoir 1701, thereby enabling process control 1705 tomonitor a level of fluid in reservoir 1701. Process control 1705 mayincrement or decrement a counter (not shown) based on each reading. Forexample, if a reading of fluid level sensor 1704 indicates that a fluidlevel in reservoir 1701 is equal to or greater than a predeterminedlevel, process control 1705 may increment counter by one. Processcontrol 1705 may increment the counter by one each time that processcontrol 1705 obtains a fluid level reading from fluid level sensor 1704indicating that the fluid level in reservoir 1701 is equal to or greaterthan the predetermined level. If a reading of fluid level sensor 1704indicates that the fluid level in reservoir 1701 is less than thepredetermined level, process control 1705 may decrement counter by one.Process control 1705 may decrement counter by one each time that processcontrol 1705 obtains a fluid level reading from fluid level sensor 1704indicating that the fluid level in reservoir 1701 is less than thepredetermined level.

Process control 1705 also monitors a value of the counter each time thatprocess control 1705 increments or decrements the counter. In oneembodiment of the invention, process control 1705 compares a value ofthe counter to one or more predetermined counter values. Thepredetermined counter values may correspond to fluid levels in reservoir1701, to fluid fill operations, or the like. For example, thepredetermined counter values may include a first counter value, whichcorresponds to a fluid level in reservoir 1701 at which fluid is addedto reservoir 1701. The predetermined counter values may include a secondcounter value, which corresponds to a fluid level in reservoir 1701 atwhich fluid is not added to reservoir 1701.

In operation, fluid level sensor 1704 detects a level of fluid inreservoir 1701 at a predetermined interval and transmits each reading toprocess control 1705. When a fluid level in reservoir 1701 decreasesbelow a predetermined level, fluid level sensor 1704 detects the fluidlevel at a predetermined interval and transmits each reading to processcontrol 1705. Process control 1705 decrements a counter each time thatprocess control 1705 obtains readings from fluid level sensor 1704indicating that the fluid level in reservoir 1701 is below apredetermined level. When process control 1705 has decremented thecounter such that a value of the counter is less than a first countervalue, process control 1705 may operate fluid supply mechanism 1703 tosupply fluid to reservoir 1701. As the fluid level in reservoir 1701increases above a predetermined level, fluid level sensor 1704 detectsthe fluid level at predetermined intervals and transmits each reading toprocess control 1705. Process control 1705 increments the counter foreach reading from fluid level sensor 1704 indicating that the fluidlevel in reservoir 1701 is equal to or greater than a predeterminedlevel. When process control 1705 has incremented the counter such that avalue of the counter exceeds a second counter value, process control1705 may operate fluid supply mechanism 1703 to stop supplying fluid toreservoir 1701.

In another embodiment of the invention, process control 1705 may queryfluid level sensor 1704 at a predetermined interval to obtain readingsof a level of fluid level in reservoir 1701. When a level of fluid inreservoir 1701 decreases below a predetermined level, fluid level sensor1704 detects the fluid level. Process control 1705 may obtain readingsof a fluid level in reservoir 1701 from fluid level sensor 1704 whenprocess control 1705 queries fluid level sensor 1704 at a predeterminedinterval. Process control 1705 decrements a counter each time thatprocess control 1705 obtains a reading indicating that the fluid levelin reservoir 1701 is below a predetermined level. When process control1705 has decremented the counter such that a value of the counter isless than a first counter value, process control 1705 may operate fluidsupply mechanism 1703 to supply fluid to reservoir 1701. As the fluidlevel in reservoir 1701 increases above a predetermined level, fluidlevel sensor 1704 detects the fluid level at predetermined intervals.Process control 1705 obtains fluid level readings from fluid levelsensor 1704 at a predetermined interval. Process control 1705 incrementsthe counter each time that process control 1705 reads fluid level sensor1704 and obtains a reading indicating that the fluid level in reservoir1701 is equal to or greater than a predetermined level. When processcontrol 1705 has incremented the counter such that a value of thecounter exceeds a second counter value, process control 1705 may operatefluid supply mechanism 1703 to stop a supply of fluid to reservoir 1701.

According to these embodiments of the invention, process control 1705may not operate fluid supply mechanism 1703 to supply fluid to reservoir1701 until the counter has been decremented below a first counter value.Thus, selection of a first counter value and a predetermined interval atwhich process control 1705 obtains fluid level readings from fluid levelsensor 1704 enables process control 1705 to precisely initiate a fluidfill operation. Moreover, during a fluid fill operation of reservoir1701, process control 1705 may not operate fluid supply mechanism 1703to stop a supply of fluid to reservoir 1701 until the counter has beenincremented above a second counter value. Thus, selection of a secondcounter value and a predetermined interval at which process control 1705obtains fluid level readings from fluid level sensor 1704 enablesprocess control 1705 to precisely terminate a fluid fill operation.Moreover, by enabling process control 1705 to precisely terminate a filloperation, the present invention eliminates or reduces the cycling offluid fill mechanism components on and off in rapid succession, therebydamaging the components in known systems and methods.

The invention will be further clarified by a consideration of thefollowing examples, which are intended to be purely exemplary of the useof the invention. In one embodiment of the invention, a first countervalue was set at sixteen, and a second counter value was set atsixty-four. Moreover, process control obtained fluid level readings froma fluid level sensor sixteen times per second, i.e., every {fraction(1/16)}th of a second. When the fluid level in the reservoir was lessthan a predetermined level, process control obtained readings from thefluid level sensor every {fraction (1/16)}th of a second, and processcontrol decremented a counter for each reading indicating that a fluidlevel in reservoir was less than the predetermined level. Once processcontrol decremented the counter to a value of fifteen, i.e., to a valueless than the first counter value of sixteen, process control operated,i.e., activated, a fluid supply mechanism to fill reservoir with fluid.Process control continued to obtain readings from the fluid level sensorevery {fraction (1/16)}th of a second. While the fluid level inreservoir remained less than the predetermined level, process controlcontinued to obtain readings from the fluid level sensor every {fraction(1/16)}th of a second and to decrement the counter for each reading.Process control continued to decrement the counter until the countervalue reached zero.

Process control continued to obtain readings from the fluid level sensorwhile operating the fluid supply mechanism to the fill reservoir withfluid. When the fluid level in the reservoir became equal to or greaterthan the predetermined level and process control obtained readings fromthe fluid level sensor indicating that the fluid level was equal to orgreater than the predetermined level, process control incremented thecounter for each such reading. Once process control incremented thecounter to a value of sixty-five, i.e., to a value greater than thesecond counter value of sixty-four, process control operated, i.e.,deactivated, fluid supply mechanism to stop supplying fluid to thereservoir. Process control continued to obtain readings from fluid levelsensor and to increment or decrement the counter accordingly. While thefluid level in the reservoir remained above the predetermined level,process control continued to obtain readings from the fluid level sensorand to increment the counter every {fraction (1/16)}th of a second.Process control continued to increment the counter for each such readinguntil the counter value reached eighty.

According to this embodiment of the invention, process control did notoperate the fluid supply mechanism to initiate a fluid fill operationuntil process control decremented the counter value to fifteen.Moreover, once process control had completed a fluid fill operation,process control did not initiate a subsequent fluid fill operation forat least three (3) seconds after the termination of a fill operation,because process control had incremented the counter to a value ofsixty-five before terminating the fluid fill operation. In fact, processcontrol did not initiate a fluid fill operation for at least three (3)seconds after process control began to obtain readings from the fluidlevel sensor indicating that the fluid level in the reservoir was lessthan the predetermined level. When the fluid level remained equal to orgreater than the predetermined level after termination of a fluid filloperation, process control continued to increment the counter until thecounter reached a value of eighty, so that process control did notinitiate a subsequent fluid fill operation for at least four (4) secondsafter process control began to obtain readings from the fluid levelsensor indicating that the fluid level in the reservoir was less thanthe predetermined level. Thus, according to this embodiment of theinvention, process control did not cycle components of the fluid supplymechanism on and off, even in those instances in which the fluid inreservoir experienced some turbulence during a fill operation, or duringheating of the fluid to produce a vapor for humidification. Of course,different values could be selected for the first counter value and thesecond counter value to provide a larger or smaller interval. Inaddition, process control could obtain fluid level readings at differentpredetermined intervals.

A heater 1706 may be positioned at reservoir 1701 to heat fluid withinreservoir 1701. For example, heater 1706 may be positioned beneathreservoir 1701, as shown in FIG. 17, to heat fluid contained inreservoir 1701. Process control 1705 may regulate heater 1706 to heatfluid in reservoir 1701, e.g., to heat fluid in reservoir 1701 to aboiling point, to produce vapor for humidifying holding cabinets.

A temperature sensor (at 1707) may be positioned at reservoir 1701 tomeasure a temperature of reservoir 1701 and to prevent damage due tooverheating of reservoir 1701 by heater 1706. Temperature sensor 1707may be integral with reservoir 1701, as shown in FIG. 17, or temperaturesensor 1707 may be positioned on an inner surface or an outer surface ofreservoir 1701 to measure a temperature of reservoir 1701. Temperaturesensor 1707 may include a plurality of sensors positioned on a surfaceof reservoir 1701 or positioned integral with reservoir 1701. Ifreservoir 1701 contains fluid, the temperature of reservoir 1701 shouldremain below a threshold temperature. If reservoir 1701 becomes empty,however, the temperature of reservoir 1701 may exceed a thresholdtemperature. Temperature sensor 1707 detects these temperature changes.

Process control 1705 communicates with temperature sensor 1707, so thatprocess control 1705 may monitor the temperature of reservoir 1701. Whentemperature sensor 1707 indicates that the temperature of reservoir 1701exceeds a threshold temperature, process control 1705 may shut offreservoir heater 1706 to avoid or reduce damage to reservoir 1701 andother components of the fluid fill system. In one embodiment of theinvention, a threshold temperature of 450° F. may be used.

FIG. 18 discloses a method of operating a fluid fill system according toan embodiment of the invention. Process control 1701 obtains fluid levelreadings from fluid level sensor 1704 at a predetermined interval (stepS1). Based on each fluid level reading obtained from fluid level sensor1704, process control 1701 determines whether a fluid level in reservoir1701 is equal to or greater than a first predetermined level (step S2).Process control 1701 increments or decrements a counter based on eachfluid level reading obtained from fluid level sensor 1704. If a fluidlevel reading indicates that the fluid level in reservoir 1701 is equalto or greater than a predetermined level, process control incrementscounter (step S3). If a fluid level reading indicates that the fluidlevel in reservoir 1701 is below a predetermined level, process control1701 decrements counter (step S4).

Process control 1701 also reads a value of the counter each time thatprocess control 1701 increments or decrements the counter (steps S5,S6). If a value of the counter is less than a first counter value (stepS5), process control 1701 may operate fluid supply mechanism 1703 tosupply fluid to reservoir 1701 (step S7). If a value of the counter isequal to or greater than a first counter value (step S5), processcontrol 1705 obtains a fluid level reading from fluid level sensor 1704(step S1). If a value of counter is greater than a second counter value(step S6), process control 1705 may operate fluid supply mechanism 1703to close fluid supply line 1702 and stop a supply of fluid to reservoir1701 (step S8). If a value of the counter is equal to or less than asecond counter value (step S6), process control 1705 obtains a fluidlevel reading from fluid level sensor 1704 (step S1).

Process control 1701 may monitor the duration of a fill operation toensure that fluid supply mechanism 1703 and other components of fluidfill system are operational. For example, process control 1701 may starta timer during a fill operation of reservoir 1701 and monitor the timethat elapses during the fill operation to determine whether the filloperation is completed within a predetermined time limit (step S9). Ifthe fill time of reservoir 1701 is less than or equal to thepredetermined time limit, process control 1705 maintains the filloperation to supply fluid to reservoir 1701 (step S11), and processcontrol 1705 obtains a fluid level reading from fluid level sensor 1704at a predetermined interval (step S1). If the fill time exceeds apredetermined time limit, process control 1701 may issue a signal (stepS10), e.g., an alarm to an equipment operator. The signal may be visualor audible, or both. The signal may advise the operator that a fluidlevel in reservoir has not reached a predetermined fill level and thatthe operator should inspect the fluid fill system, e.g., the fluidsupply line, the fluid supply mechanism, the fluid level sensor, or thelike, to ensure that the system components are operational. For example,process control 1705 may issue a message “water pan not filling, checkwater supply.” The signal may continue until process control 1705obtains a reading from fluid level sensor 1704 indicating that the fluidlevel in reservoir 1701 is equal to or greater than a predeterminedlevel. In an embodiment of the invention, the timer may be reset whenprocess control 1705 is shut down or restarted.

Process control 1705 may communicate with temperature sensor 1707 (stepS12) to determine whether the temperature of reservoir 1701 exceeds athreshold temperature. If process control 1705 obtains readings fromtemperature sensor 1707 indicating that the temperature of reservoir1701 is equal to or less than a threshold temperature, process control1705 continues to obtain fluid level readings from fluid level sensor1704 (step S1). If the temperature of reservoir 1701 is greater than athreshold temperature, process control 1705 may issue a signal (stepS13), e.g., an alarm, or the like, to an operator. The signal may bevisual or audible, or both. The signal may advise an operator thatreservoir 1701 may be empty. For example, process control may issue amessage “no water, float switch failed.” Process control 1705 also turnsoff reservoir heater 1706 (step S14). Process control 1705 may turn offreservoir heater 1706 irrespective of a status of fluid level sensor1704 and a value of the counter. This procedure reduces or preventsdamage to system components in the event that fluid level sensor 1704becomes inoperative or otherwise fails to indicate that reservoir 1701is empty.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of this specification or a practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

We claim:
 1. A fluid fill system comprising: at least one sensor fordetecting whether a fluid level in a reservoir is equal to or greaterthan a predetermined fluid level; and a process control, wherein saidprocess control obtains a reading from said at least one sensor at apredetermined interval and increments a counter if said readingindicates that said fluid level is equal to or greater than saidpredetermined fluid level and decrements said counter if said readingindicates that said fluid level is less than said predetermined fluidlevel, and wherein said process control operates a fluid supplymechanism when a value of said counter moves beyond a predeterminedvalue.
 2. The system of claim 1, wherein said predetermined valueincludes a first counter value, and wherein said process controloperates said fluid supply mechanism to supply fluid to said reservoirwhen said process control decrements said counter below said firstcounter value.
 3. The system of claim 1, wherein said predeterminedvalue includes a second counter value, and wherein said process controloperates said fluid supply mechanism to stop supplying fluid to saidreservoir when said process control increments said counter above saidsecond counter value.
 4. The system of claim 3, wherein said processcontrol operates said fluid supply mechanism to stop supplying fluid tosaid reservoir, after a predetermined time elapses, even if said processcontrol has not incremented said counter above said second countervalue.
 5. The system of claim 4, wherein said process control issues asignal when said predetermined time elapses.
 6. The system of claim 1,wherein said at least one sensor comprises a float switch.
 7. The systemof claim 1, wherein said fluid supply mechanism comprises: a fluidsupply line; and a solenoid valve, wherein said process control operatessaid solenoid valve to open or close said fluid supply line.
 8. Thesystem of claim 1, wherein said predetermined interval comprises a rangeof intervals.
 9. The system of claim 1, further comprising: a heater forheating said fluid in said reservoir; and a temperature sensor formeasuring a temperature of said reservoir, wherein said process controlobtains readings from said temperature sensor and deactivates saidheater when said reservoir temperature exceeds a threshold temperature.10. The system of claim 9, wherein said temperature sensor is integralwith said reservoir.
 11. The system of claim 9, wherein said processcontrol issues a signal when said reservoir temperature exceeds saidthreshold temperature.
 12. A method of filling a reservoir with fluid,comprising the steps of: obtaining a fluid level reading at apredetermined interval to determine whether a fluid level in a reservoiris equal to or greater than a predetermined level; incrementing acounter if said fluid level reading is equal to or greater than saidpredetermined level; decrementing said counter if said fluid levelreading is less than said predetermined level; and operating a fluidsupply mechanism when a value of said counter moves beyond apredetermined value.
 13. The method of claim 12, wherein saidpredetermined value comprises a first counter value, and wherein thestep of operating said fluid supply mechanism comprises the step ofsupplying fluid to said reservoir when said process control decrementssaid counter below said first counter value.
 14. The method of claim 12,wherein said predetermined value comprises a second counter value, andwherein the step of operating said fluid supply mechanism comprises thestep of stopping a flow of fluid to said reservoir when said processcontrol increments said counter above said second counter value.
 15. Themethod of claim 14, further comprising the step of: stopping a flow offluid to said reservoir after a predetermined time has elapsed even ifsaid process control has not incremented said counter above said secondcounter value.
 16. The method of claim 15, further comprising the stepof: issuing a signal when said predetermined time elapses.
 17. Themethod of claim 12, wherein the step of obtaining fluid level readingsat a predetermined interval comprises the step of obtaining fluid levelreadings in a range of predetermined intervals.
 18. The method of claim17, further comprising the step of: issuing a signal when saidtemperature exceeds said threshold temperature.
 19. The method of claim12, further comprising the steps of: heating said reservoir; measuring atemperature of said reservoir; and stopping a heating of said reservoirwhen said temperature exceeds a threshold temperature.
 20. The method ofclaim 12, wherein the step of operating a fluid supply mechanismincludes the step of operating a solenoid valve to open or close a fluidsupply line.